In semiconductor manufacturing processes, sulfuric acid is used, either alone or in combination with other substances, for different purposes, for example, for cleaning silicon substrates, removing resist films or formulating etching solutions.
The increased density of integrated circuits nowadays has inevitably led to micronization of patterns and complication of the (trench structure (i.e. fine deep grooves). Use of conventional sulfuric acid under these condition gives rise to inconveniences such as difficult permeation into trenches and insufficient cleaning, due to high surface tension and poor wettability. Accordingly it is now strongly desired to develop a sulfuric acid composition with low surface tension and good wettability.
Although use of surface-active agent is expected to lower the surface tension of sulfuric acid, only very limited types of surface-active agent are stable in hot sulfuric acid, in particular, in highly oxidizing sulfuric acid/hydrogen peroxide liquid mixtures, with the result that it is in fact extremely difficult to find such surface-active agents that can be put into practical use.
As a result of research on a variety of surfaceactive agents, the inventors have found that specific ones amongst many fluorine-type surface-active agents are stable in hot liquid mixtures of sulfuric acid and hydrogen peroxide and capable of lowering the surface tension. The present invention bases itself on these findings.